Another Double Cross Antenna build (went wrong)
Posted: Wed Apr 10, 2019 12:39 pm
Hello guy's! Since im from germany, my english is not the best but i hope you can help me with my problem!
First of all, this isn't the first double cross antenna i've build. The first one was a one day holiday project, meant to last only a few days, so no expensive materials were used. I even forgot about the velocity factor in the coax line
Surprisingly this antenna worked pretty good, and i received some meteor images. Since i didn't use an LNA, the signal was very weak below 20 degrees altitude.
----
Now, one year later, i've build a new one out of pvc pipes to withstand the weather, everything sealed waterproof. I even bought a noaa saw filtered lna to get a stronger signal. Powered over bias with a nooelec smartee
After some first test i was pretty impressed, even below 10 degrees i was able to decode a picture using Sdr#, Meteor Demodulator and DDE plugin. I received pictures of greenland, iceland, sweden, russia, england and also part of africa
Now comes the strange part: as the satellite is raising over the horizon, the signal gets strong pretty quick, apart from some radiation nulls caused by our roof. As soon as it hits >80 degrees, the signal gets weak (even pulsing a bit), resaulting in lost lines across the image. Seems like there's a huge radiation null
--- After doing some research i noticed that i wired all four dipoles upside down, meaning the center conductor is connected to the lower part.
--- Since i made this mistake with all four, it shouldn't be big of a deal?.. or is it?
Second problem is another radiation null located at south, maybe caused by our satellite dish? I'm able to get pictures of iceland, which is pretty far north, but africa is nearly impossible. Would like to fix that too
Here are some details about the antenna:
4mm2 blank cooper wire, cut to length (545mm each, two per dipole, so every dipole is 1090mm long)
RG58 coax (with a velocity factor of 0,66) cut to two pieces of 400mm, and two to 760mm, so 1/4 longer
Each pair of dipoles is spaced apart exactly 1/4 of a wavelength!
Pvc pipes do not contain any metal materials (to add strength for example)
Well that's it for now, i hope some kind person could help me with that problem! If you need more details or pictures, feel free to request them
P.s.: North is marked on the antenna by the red velcro!
First of all, this isn't the first double cross antenna i've build. The first one was a one day holiday project, meant to last only a few days, so no expensive materials were used. I even forgot about the velocity factor in the coax line
Surprisingly this antenna worked pretty good, and i received some meteor images. Since i didn't use an LNA, the signal was very weak below 20 degrees altitude.
----
Now, one year later, i've build a new one out of pvc pipes to withstand the weather, everything sealed waterproof. I even bought a noaa saw filtered lna to get a stronger signal. Powered over bias with a nooelec smartee
After some first test i was pretty impressed, even below 10 degrees i was able to decode a picture using Sdr#, Meteor Demodulator and DDE plugin. I received pictures of greenland, iceland, sweden, russia, england and also part of africa
Now comes the strange part: as the satellite is raising over the horizon, the signal gets strong pretty quick, apart from some radiation nulls caused by our roof. As soon as it hits >80 degrees, the signal gets weak (even pulsing a bit), resaulting in lost lines across the image. Seems like there's a huge radiation null
--- After doing some research i noticed that i wired all four dipoles upside down, meaning the center conductor is connected to the lower part.
--- Since i made this mistake with all four, it shouldn't be big of a deal?.. or is it?
Second problem is another radiation null located at south, maybe caused by our satellite dish? I'm able to get pictures of iceland, which is pretty far north, but africa is nearly impossible. Would like to fix that too
Here are some details about the antenna:
4mm2 blank cooper wire, cut to length (545mm each, two per dipole, so every dipole is 1090mm long)
RG58 coax (with a velocity factor of 0,66) cut to two pieces of 400mm, and two to 760mm, so 1/4 longer
Each pair of dipoles is spaced apart exactly 1/4 of a wavelength!
Pvc pipes do not contain any metal materials (to add strength for example)
Well that's it for now, i hope some kind person could help me with that problem! If you need more details or pictures, feel free to request them
P.s.: North is marked on the antenna by the red velcro!